Advanced Thermoplastics for Orthodontics

ABSTRACT

An orthodontic archwire comprising a thermoplastic polymer. In some embodiments the thermoplastic polymer is a rigid backbone polymer including at least one of a compatibilizing side group or a solubilizing side group. The thermoplastic polymer may be heat processed to form the orthodontic archwire.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/656,237, filed Jan. 22, 2007, which is a division of U.S.patent application Ser. No. 10/612,511, filed Jul. 2, 2003, which claimsthe benefit of U.S. Provisional Application No. 60/393,791, filed Jul.3, 2002, the contents of each of which are incorporated herein byreference in their entirety.

FIELD

The present invention relates generally to polymer comprisingorthodontic devices. One aspect of the present invention is moreparticularly concerned with new and improved polymer comprisingorthodontic components and appliances.

BACKGROUND

As is well known, orthodontic appliances are used to move or manipulatecertain teeth to correct irregularities and/or abnormalities in theirrelationships with surrounding members. Orthodontic appliances includesystems comprising wires and brackets as well as systems comprisingremovable aligners. This manipulation is achieved by the application ofdesigned force systems to selected teeth. The forces for these systemsare provided by a force delivery component such as an arch wire orspring. The wire is elastically deformed, or activated, to absorbenergy. The wire slowly releases this energy as it deactivates andreturns to the relaxed condition. The released energy is applied toselected teeth, for instance by interaction of the loaded wire withbrackets attached to the teeth, to provide the desired tooth movement.

Tooth movement can best be achieved by producing an optimal force systemcapable of delivering relatively light but continuous corrective forces.Some desirable biomechanical characteristics of the orthodontic forcesystem include low to moderate force magnitude, constancy of forcemagnitude during deactivation and accurate location of the forceapplication point. The use of a low to moderate force magnitude willallow the teeth to move rapidly and relatively painlessly with minimumtissue damage. A constant force magnitude over time will provide maximumtissue response. Additionally, if the orthodontic appliance releasesforce too rapidly, it becomes more difficult to accurately produce thedesired effect, requiring more frequent adjustments to maintain theforce at some minimum desired level.

There are several additional criteria that are important for orthodonticappliances in general. For example, the orthodontic material must benon-toxic, resistant to the corrosive environment within a patient'smouth and available in desired shapes and dimensions. Some otherimportant parameters, especially for orthodontic force deliverycomponents, include strength, elastic deformation, yield strength,stiffness, formability and joinability. More recently, the aestheticappearance of orthodontic components has become very important, withmany patients expressing a strong preference for orthodontic componentsand appliances that are less visually apparent against the patient'steeth.

Elastic deformation or “spring back” is a measure of the amount ofdeflection or activation that the wire or other component can sustainand still be totally elastic, that is, to recover to its original shapeand position. The elastic deformation of an orthodontic component isfundamentally proportional to its ratio of flexure strength to flexuremodulus; or similarly its ratio of tensile yield strength to modulus ofelasticity. The higher the ratio of yield strength to modulus, thegreater the elastic deformation. Design factors also affect elasticdeformation, for example, the elastic deformation of round wire variesinversely as the first power of the diameter and the second power of thelength of the wire. Elastic deformation is important because itdetermines the distance over which an appliance can provide an effectiveforce system before readjustment is necessary. Appliances that cansustain larger elastic deformation (deflection) can more readily engageteeth that are severely malposed.

Yield strength must be high enough to assure achieving desired forcelevels for tooth movement and preventing appliance failure associatedwith permanent deformation. The lack of adequate yield strength can notbe corrected by design changes such as increase in size or bulk becauseof size limitations in the oral cavity. Metals have traditionally beenused in orthodontics because in the necessary cross-sections theyprovide desirable force levels that other categories of structuralmaterials, such as engineering plastics, have not been able to provide.

Stiffness is the ratio of force/unit activation. The stiffness orrigidity of an appliance varies significantly with appliance design, forexample, stiffness varies as the fourth power of the diameter for roundwire. For rectangular wire, stiffness varies as bd³, where b is the baseor cross-sectional dimension perpendicular to the force and d is thedepth or cross-sectional dimension parallel to the force. Wires ofunique cross-sections, such as polygonal, offer different stiffnesses,and hence different forces, in different planes. Although not availablewith metal appliances, it is desirable for an appliance to have uniquecross-sectional shapes that give greater control over tooth movement byvarying force as required in the three dimensional planes.

The stiffness of an appliance component, when stiffness is linear in therange of use, is a primary determinant of the force that can be appliedto teeth during manipulation. Greater stiffness results in more forcefor each unit of activation. Generally, low stiffness orthodonticcomponents are required for active tooth movement and high stiffnesscomponents for passive holding components. High stiffness may berequired for small deflection applications. For example, if a tooth were4 mm out of alignment and 100 g of force is needed, 25 g/mm would be alow stiffness and 1,000 g/mm would be a high stiffness.

Some orthodontic components, such as a wire, require sufficientductility to be formed to a desired customized shape for a particularpatient. Additionally, the wire has to be joinable to other wires orcomponents, while retaining its strength and elasticity characteristics.Naturally, the wire must be available in a variety of desiredcross-sectional shapes and dimensions as variability in cross-sectionalshape can allow greater potential control of orthodontic force systems.All orthodontic wires have conventionally had either rectangular orcircular cross sections.

Some orthodontic components, such as attachments, that translate theforce from the wire directly to the tooth have additional criteria thathave to be considered. For example, the design, geometry and overalldimensions of an attachment such as a bracket are important for both itsease of manipulation as well as its ability to help contribute toeffective application of the orthodontic force system. Attachments maybe bonded directly to the tooth surface or mechanically fastened using aband that typically circumscribes the entire tooth. An attachment thatis bonded may have certain functional shapes and contours on the surfacecontacting the tooth in order to aid adhesion. Attachments should beeasy to fabricate or manufacture. Attachments must have sufficientstrength to transfer force to the joined tooth without attachmentdeformation or fracture. Additionally, it is desirable for the bracketto be comprised of a material that provides a low level of friction towires within the slot. Aesthetics of attachments are again veryimportant to some patients.

There have been attempts to use material selection in conjunction withappliance design to control orthodontic force systems. Over the yearsdental practitioners have used orthodontic force delivery componentsmade from gold alloys, stainless steel alloys, nickel-titanium memorytype alloys of the type described in U.S. Pat. No. 4,037,324 and betatitanium alloys of the type described in U.S. Pat. No. 4,197,643 in aneffort to design orthodontic components that can impart a desired forcesystem. While the above materials have been successfully used fororthodontic applications, some deficiencies remain.

Orthodontic component aesthetics is an increasingly importantconsideration, particularly for labial appliances and components. Metalcomponents have a characteristic gray or silver color that is quiteobvious against the color background of the tooth structure andaesthetically objectionable to many patients. The use of clear ortooth-colored components and appliances would be considerably moreaesthetically pleasing to many patients. Attempts have been made toovercome the aesthetic deficiencies of metal orthodontic components.Tooth colored plastic coatings have been applied to the metalcomponents. Such coatings can lose adhesion to the underlying metalsurface and peel off; exhibit an undesirably high amount of frictionwhen used with metal or ceramic brackets and are relatively soft and canbe scraped or gouged by contact with harder surfaces.

Metallic orthodontic components have also specifically been identifiedas a problem area for the nuclear magnetic resonance diagnosticprocedure, since metals do not exhibit the requisite radiolucency andinterfere with the resulting images.

There have also been attempts to use material selection to improvecharacteristics of other orthodontic components. Brackets have beenfabricated from ceramic materials in an attempt to provide a moreaesthetically pleasing appliance. However, ceramic brackets, whileavailable, are expensive; are not available in more complex shapes andsizes; are brittle; and are very hard and can wear contacting teeth.Ceramic brackets may also be difficult to debond, leading to toothenamel fracture.

Another approach to orthodontic tooth movement is the use of a removableappliance, such as an aligner, in place of wires and brackets. Suchaligners can be very aesthetic and “patient friendly” since they areremovable by the patient and require no bonding of attachments. Onelimitation of current materials with respect to aligners is theoccurrence of permanent deformation adjacent to the imprint of the finalcrown position, which does not allow exact tooth movement because theshape of the aligner has been altered and no longer applies the requiredforce. This permanent deformation is related to inadequate mechanicalproperties of available materials used in removable appliances, forexample yield strength and modulus.

It is generally believed that thermoplastic polymers such aspolymethylmethacrylate (PMMA) or polycarbonate and even high strengthpolymers such as polyetheretherketone (PEEK) do not possess therequisite flexural strength, modulus and elastic deformation desirable,or in some cases necessary, for use as a force delivery component. Table1 lists the mechanical properties of some known high strengthengineering polymers as well as properties for some metals useful inorthodontic use.

TABLE 1 Flexure Flexure Strength, Tensile Tensile Strength, Modulus, MPaModulus, MPa Material GPa Yield GPa Yield Ultimate Poly- 6.6 221 5.8 160benzimidazole (PBI) Polyamide-imide 5.2 185 (PAI) Polyphenylene 3.8 963.8 65 sulfide (PPS) Poly- 4.1 170 3.5 97 120 etheretherketone (PEEK)Polyether-imide 3.3 118 3.3 103 (PEI) Polymethyl- 2.3 91 2.5 51 53methacrylate (PMMA) Polycarbonate 2.8 88 2.3 62 70 (PC) Acrylonitrile-2.5 83 2.3 50 butadiene- styrene (ABS) Polyamides 1.8 80 1.9 60 75(nylon) Thermoplastic 0.5 1.2 37 Polyurethane Nickel-Titanium 41.4 1489Beta Titanium 71.7 1276 Stainless Steel 179.0 2117

Brackets have been fabricated from polycarbonate materials in an attemptto provide a more aesthetically pleasing appliance. However,polycarbonate brackets cannot resist the high stress magnitudesfrequently encountered in orthodontics so that the bracket slot distortsor spreads apart under torque loading well below the levels desirablefor clinical use. In addition, polycarbonate brackets have tying wingsthat have been known to fail. Polycarbonate as an orthodontic materialcan also stain from contact with food.

More recently, highly fiber reinforced composite materials such as thosedescribed in U.S. Pat. No. 4,717,341 have been proposed for use inorthodontics. Such highly fiber reinforced composite materials showpromise in this application, however, these materials presently areanisotropic, are somewhat difficult to form into complex shapes, requireeffective coupling of the high strength reinforcing phase into thepolymer matrix and have low ductility.

SOME DEFINITIONS USED IN THE SPECIFICATION

The following terms will have the given definitions unless otherwiseexplicitly defined.

Elastic deformation or spring back—the amount of deflection oractivation that the wire or other component can sustain and still betotally elastic, that is, to recover to its original shape and position.

Filler material—Particles, powder or other materials having havingapproximately equal dimensions in all directions. Filler material isadded to a polymer primarily to enhance polymer properties such as wearresistance, mechanical properties or color.

Neat—Without admixture or dilution, that is substantially free ofmaterials such as additives, filler materials, other polymers,plasticizers and reinforcing agents.

Non-Thermoplastic polymer—Any polymer which does not fall within thedefinition of a thermoplastic polymer.

Orthodontic appliance—A device used for tooth alignment, occlusalcorrection and non-surgical jaw alteration. Appliances can be fixed orremovable. Removable appliances, such as aligners, are inserted andremoved by the patient.

Orthodontic attachment—Brackets, tubes or other shapes bonded to a toothor to a band that joins an orthodontic wire with the tooth.

Orthodontic auxiliary—Items added to supplement an appliance, includingsprings separate from the arch wire and hooks and buttons joined to awire or tooth.

Orthodontic component—Any part of a fixed or removable appliance, forexample attachments, wires, ligating mechanisms and auxiliaries.

Orthodontic force delivery component. —Any part of an orthodonticappliance that is capable of storing energy for tooth movement.

Orthodontic ligating mechanism—Mechanism such as metal ligature wires,elastomeric rings or caps for joining wires to an attachment.

Orthodontic wire—A force delivery component of the appliance.

Polymer—A long chain of covalently bonded, repeating, organic structuralunits. Generally includes, for example, homopolymers, copolymers, suchas for example, block, graft, random and alternating copolymers,terpolymers, etc, and blends and modifications thereof. Furthermore,unless otherwise specifically limited, the term “polymer” includes allpossible geometric configurations. These configurations include, forexample, isotactic, syndiotactic and random symmetries.

Reinforcing agent—a filament, fiber, whisker, insert, etc. having alength much greater than its cross sectional dimensions. Reinforcingagents are primarily used to increase the mechanical properties of apolymer.

Stiffness—The ratio of a steady force acting on a deformable elasticmaterial to the resulting displacement of that material.

Thermoplastic polymer—A polymer that is fusible, softening when exposedto heat and returning generally to its unsoftened state when cooled toroom temperature. Thermoplastic materials include, for example,polyvinyl chlorides, some polyesters, polyamides, polyfluorocarbons,polyolefins, some polyurethanes, polystyrenes, polyvinyl alcohol,copolymers of ethylene and at least one vinyl monomer (e.g., poly(ethylene vinyl acetates), cellulose esters and acrylic resins.

Unreinforced—A material with substantially no reinforcing agent.

SUMMARY

Briefly, one aspect of the invention is an orthodontic componentcomprised of a thermoplastic polymer wherein the thermoplastic polymerin the neat resin form has an unreinforced tensile strength of at leastabout 150 MPa and an unreinforced tensile modulus of at least about 4GPa. In one embodiment the component comprises a rigid backbone polymer.In another embodiment the inventive component is an orthodontic forcedelivery component.

Another aspect of the invention is an orthodontic appliance comprised ofa thermoplastic polymer wherein the thermoplastic polymer in the neatresin form has an unreinforced tensile strength of at least about 150MPa and an unreinforced tensile modulus of at least about 4 GPa. In oneadvantageous embodiment all of the components of the appliance arecomprised of a rigid backbone polymer. In another embodiment theinventive orthodontic appliance includes components comprised of a rigidbackbone polymer as well as components comprised of other materials.

Yet another aspect of the present invention is the provision of anorthodontic component or an orthodontic appliance having an improvedaesthetic appearance. The components and appliances are fabricated froma thermoplastic polymer having a refractive index of about 1.66 to about1.70. The thermoplastic polymer ranges from transparent to translucentand may include fillers, additives or other materials to approximate thecolor of a patient's tooth. In one embodiment the component comprises arigid backbone polymer.

Still another aspect of the invention is a method of manufacturing anorthodontic component comprising heating a thermoplastic polymer to asoftened state and forming the softened thermoplastic polymer into anorthodontic component.

In general, unless otherwise explicitly stated the material of theinvention may be alternately formulated to comprise, consist of, orconsist essentially of, any appropriate components herein disclosed. Thematerial of the invention may additionally, or alternatively, beformulated so as to be devoid, or substantially free, of any components,materials, ingredients, adjuvants or species used in the prior artcompositions or that are otherwise not necessary to the achievement ofthe function and/or objectives of the present invention.

A better understanding of the invention will be obtained from thefollowing detailed description and the accompanying drawings as well asfrom the illustrative applications of the invention including theseveral components of the invention and the relation of one or more ofsuch components with respect to each of the others as well as to thefeatures, characteristics, compositions, properties and relation ofelements described and exemplified herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will be evident to one ofordinary skill in the art from the following detailed description madewith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of an inventive forcedelivery component engaged within slots of an inventive bracket.

FIG. 2 is an illustration of a portion of one embodiment of an installedorthodontic appliance showing a pair of conventional brackets with aninventive force delivery component engaged within slots in each of thebrackets.

FIG. 3 is a schematic illustration of a portion of an orthodonticappliance showing an elastically deformed force delivery componentreleasing energy to a pair of bonded brackets.

FIGS. 4 a-4 d are cross sectional representations illustrating someembodiments of some inventive orthodontic components.

FIGS. 5 a-5 b are schematic illustrations showing some shapedembodiments of inventive force delivery components.

FIG. 6 is a cross sectional illustration of one embodiment of aninventive torsional force delivery component releasing energy to oneembodiment of an inventive bracket.

FIG. 7 is a cross sectional representation of one embodiment of aninventive wire having a shape configured to register within a matingbracket slot.

FIG. 8 is a cross sectional representation illustrating three inventivewire embodiments each having shapes configured to register within amating bracket slot.

FIG. 9 is a cross sectional representation of one embodiment of theinvention illustrating an inventive retaining cap securing an inventivewire within a bracket slot.

FIG. 10 is a cross sectional representation of one embodiment of theinvention illustrating an inventive integral retaining cap and wire.

FIG. 11 is a front view of one embodiment of the invention illustratingan inventive ligating spring securing an inventive wire within a slot ofa bracket.

FIG. 12 a is a cross sectional representation of one embodiment of aninventive tube with an attached hook.

FIG. 12 b is a front view of the tube of FIG. 12 a.

FIG. 13 is a cross sectional representation of one embodiment of aninventive orthodontic auxiliary including a hook.

FIG. 14 is a perspective view of a test bracket.

FIG. 15 is a graph of stiffness and bracket width for some inventive andcomparative (polycarbonate) brackets.

FIG. 16 is a graph showing maximum torque for some inventive andcomparative (polycarbonate) brackets.

FIG. 17 is a graph showing maximum stiffness for some inventive andcomparative (polycarbonate) wires.

FIG. 18 is a graph showing maximum moment for some inventive andcomparative (polycarbonate) wires.

FIG. 19 is a graph showing load-deflection curves for some inventiveorthodontic components.

FIG. 20 schematically illustrates an inventive archwire formed by heatprocessing.

FIGS. 21 a, 21 b and 21 c each illustrate the placement and use of aninventive archwire in an orthodontic appliance installed on a model.

FIG. 22 schematically illustrates placement and use of upper and lowerarchwires in an orthodontic appliance.

FIG. 23 schematically illustrates use of an inventive archwire as partof an orthodontic appliance before orthodontic correction.

FIG. 24 schematically illustrates use of the inventive archwire of FIG.23 after orthodontic correction.

FIG. 25 schematically illustrates use of an inventive force deliverycomponent as part of an orthodontic appliance before orthodonticcorrection.

FIG. 26 schematically illustrates use of the inventive force deliverycomponent of FIG. 25 after the orthodontic correction.

FIG. 27 schematically illustrates a removable orthodontic aligner withvarying stiffness at the incisal and gingival portions to effect lingualroot movement.

FIG. 28 schematically illustrates an inventive force delivery componentincorporated into a removable aligner.

DETAILED DESCRIPTION

In contrast to the prevailing knowledge in the art, it has now beendiscovered that certain thermoplastic polymers surprisingly do possessthe requisite combination of tensile strength, tensile modulus andelastic deformation to provide orthodontic force magnitudes at least atthe lower to intermediate range of forces produced by conventional metalappliances. Thus one aspect of the present invention is the use ofthermoplastic polymer materials to produce an orthodontic component,including (with reference to FIG. 1), for example, a force deliverycomponent 12, an attachment 14, an auxiliary 16 (shown in FIG. 13) and aligating mechanism 18 (shown in FIG. 11). The inventive components canbe used, with or without conventional orthodontic components, to formnovel orthodontic appliances 20 such as shown in FIG. 2.

One class of polymers useful in the present invention are the rigidbackbone polymers. As used herein, the term rigid backbone polymerencompasses any of a “rigid-rod polymer”, a “segmented rigid-rodpolymer”, a “semi-rigid-rod polymer” or a combination thereof. Rigidbackbone polymers have a backbone at least partially comprising aryleneor heteroarylene moieties covalently bonded to each other. U.S. Pat.Nos. 5,886,130 (Trimmer et al.) and 6,087,467 (Marrocco, III. et al.),the contents of which are incorporated by reference herein, providefurther description of some rigid backbone polymers. Parmax® 1000 andParmax® 1200, available from Mississippi Polymer Technologies, Inc. ofBay St. Louis, Miss., are representative of some rigid backbone polymermaterials found useful in practice of the invention. Rigid backbonepolymers have a surprisingly unique balance of properties for use inorthodontic applications, that require high mechanical properties,formability, thermoplastic processing capability and sometimestranslucency. In orthodontic applications, the mechanical properties ofunreinforced rigid backbone polymers are sufficient to deliver thenecessary biomechanical forces, a level only possible with certain otherpolymers when a second phase, high strength reinforcement, such asfibers, are used. The absence of reinforcing fibers or particlesprovides high ductility and ease of processing both for the clinicianand the manufacturer, while maintaining a high degree of clarity, makingfor outstanding aesthetics. In addition, since the subject polymer is athermoplastic there is for the first time the potential of using variousthermal processing methods, such as injection molding, compressionmolding or extrusion to form orthodontic components with various shapesand geometries. For example, the geometry and size of an inventivearchwire can be varied along its length, creating endless, novelpossibilities for control of forces.

Rigid-rod polymers are comprised of phenylene monomer units joinedtogether by carbon-carbon covalent bonds, wherein at least about 95% ofthe bonds are substantially parallel to each other. Preferably, thecovalent bonds between monomer units are 1,4 or para linkages so thateach monomer unit is paraphenylene. Each paraphenylene monomer unit canbe represented by the following structure.

This molecular arrangement of paraphenylene groups, while able to rotateabout its long axis, cannot bend or kink as is possible with most otherengineering polymer backbones, imparting high mechanical properties.

A polymer consisting only of rigid-rod macromonomers would not besoluble, making synthesis very difficult and thermal processingimpossible. Accordingly, each of R₁, R₂, R₃ and R₄ is independentlychosen from H or an organic solubilizing group. The number and size ofthe organic solubilizing groups chosen being sufficient to give themonomers and polymers a significant degree of solubility in a commonsolvent system. As used herein, the term “soluble” means that a solutioncan be prepared containing greater than 0.5% by weight of the polymerand greater than about 0.5% of the monomer(s) being used to form thepolymer. As used herein, the term “solubilizing groups” means functionalgroups which, when attached as side chains to the polymer in question,will render it soluble in an appropriate solvent system. Parmax® 1000(poly-1,4 (benzoylphenylene)), available from Mississippi PolymerTechnologies, Inc., is one example of a rigid-rod polymer.

Segmented rigid-rod polymers are polymers that comprise both rigid-rodsegments comprised of rigid-rod monomer units (defined above) andnon-rigid-rod segments in the backbone of the polymer. The segmentedrigid-rod polymer has the following structure:

represents the rigid-rod monomer segment described above and therepeating [A] units are other than the rigid-rod segments. The averagelength of the rigid-rod segment (n) is about 8 monomer units, while theaverage length of the non rigid-rod segment (m) is at least 1. Each ofR₁, R₂, R₃ and R₄ is independently chosen from H or an organicsolubilizing group.

Semi-rigid-rod polymers include a backbone comprising (1,4) linkedparaphenylene monomer units and non-parallel, phenylene monomer units.Preferably, the non-parallel phenylene monomer units comprise (1,3) ormeta phenylene polymer units. By introducing non-parallel phenylenerepeat units, specifically meta-phenylene repeat units, solubility andprocessability can be maintained with fewer solubilizing groups (R₁-R₄)than are required for rigid-rod polymers. These semi-rigid-rod polymers,with fewer parallel paraphenylene units in the backbone are at mostsemi-rigid and do not have the extremely high viscosity characteristicsof rigid-rod polymers, yet still have mechanical properties superior tostandard engineering thermoplastics. One example of a para and metastructure is a random co-polymer of benzoyl appended 1,4-phenylene and1,3-phenylene, which is similar in structure to the commercial polymerParmax® 1200 available from Mississippi Polymer Technologies, Inc.

In some embodiments, the properties for rigid backbone polymers such astensile strength and tensile modulus are dependent on the chemicalstructure of the polymer and processing conditions used to prepare thepolymer. Alteration of the monomer components and monomer componentratios is believed to allow lower values for properties such as tensilestrength and tensile modulus. For example, the monomer component ratioscould be altered to achieve a rigid backbone polymer having a neat resintensile strength of about 150 MPa or lower and a neat resin tensilemodulus of about 4 GPa or lower.

All three classes of rigid backbone polymers use solubilizing sidegroups to some extent. It is well known that it is difficult a priori toselect an appropriate solvent, thus various factors will determine theeffectiveness of the selected solubilizing groups. Such factors includethe nature of the backbone itself, the size of the solubilizing groups,the orientation of the individual monomer units, the distribution of thestabilizing groups along the backbone, and the match of the dielectricconstants and dipole moments of the solubilizing groups and the solvent.Nevertheless, general strategies have been developed. For example, ifthe rigid-rod or segmented rigid-rod polymers are to be synthesized inpolar solvents, the pendant solubilizing groups of the polymer and themonomer starting material will be a group that is soluble in polarsolvents. Similarly, if the rigid-rod or segmented rigid-rod polymersare to be synthesized in non-polar solvents, the pendant solubilizinggroup on the rigid-rod polymer backbone and the monomer startingmaterial will be a group that is soluble in non-polar solvents.

Solubilizing groups which can be used include, but are not limited to,alkyl, aryl, alkaryl, aralkyl, alkyl amide, aryl amide, alkyl thioether,aryl thioether, alkyl ketone, aryl ketone, alkoxy, aryloxy, benzoyl,cyano, fluorine, heteroaryl, phenoxybenzoyl, sulfone, ester, imide,imine, alcohol, amine, and aldehyde. These solubilizing groups may beunsubstituted or substituted as described below. Other organic groupsproviding solubility in particular solvents can also be used assolubilizing groups. In some embodiments adjacent solubilizing groupsmay be bridging.

Additional pendant solubilizing side groups include alkylester,arylester, alkylamide and arylamide acetyl, carbomethoxy, formyl,phenoxy, phenoxybenzoyl, and phenyl. Further solubilizing side groupsmay be chosen from F, —CN, —CHO, —COR, —CR═NR′, —OR, —SR, —SO₂R, —OCOR,—CO₂R, —NRR′, —N═CRR′, —NRCOR′, —CONRR′, and R, where R and R′ are eachselected independently from the group consisting of H, alkyl,substituted alkyl, aryl, substituted aryl, heteroaryl and substitutedheteroaryl.

Unless otherwise specifically defined, alkyl refers to a linear,branched or cyclic alkyl group having from 1 to about 9 carbon atomsincluding, for example, methyl, ethyl, propyl, butyl, hexyl, octyl,isopropyl, isobutyl, tert-butyl, cyclopropyl, cyclohexyl, cyclooctyl,vinyl and allyl. Linear and branched alkyl group can be saturated orunsaturated and substituted or unsubstituted. A cyclic group issaturated and can be substituted or unsubstituted.

Unless otherwise specifically defined, aryl refers to an unsaturatedring structure, substituted or unsubstituted, that includes only carbonas ring atoms, including, for example, phenyl, naphthyl, biphenyl,4-phenoxyphenyl and 4-fluorophenyl.

Unless otherwise specifically defined, heteroaryl refers to anunsaturated ring structure, substituted or unsubstituted, that hascarbon atoms and one or more heteroatoms, including oxygen, nitrogenand/or sulfur, as ring atoms, for example, pyridine, furan, quinoline,and their derivatives.

Unless otherwise specifically defined, heterocyclic refers to asaturated ring structure, substituted or unsubstituted, that has carbonatoms and one or more heteroatoms, including oxygen, nitrogen and/orsulfur, as ring atoms, for example, piperidine, morpholine, piperazine,and their derivatives.

Unless otherwise specifically defined, “alcohol” refers to the generalformula alkyl-OH or aryl-OH.

Unless otherwise specifically defined, “ketone” refers to the generalformula —COR including, for example, acetyl, propionyl, t-butylcarbonyl,phenylcarbonyl (benzoyl), phenoxyphenylcarbonyl, 1-naphthylcarbonyl, and2-fluorophenylcarbonyl.

Unless otherwise specifically defined, “amine” refers to the generalformula —NRR′ including, for example, amino, dimethylamino, methylamino,methylphenylamino and phenylamino.

Unless otherwise specifically defined, “imine” refers to the generalformula —N═CRR′ including, for example, dimethyl imino (R and R′ aremethyl), methyl imino (R is H, R′ is methyl) and phenyl imino (R is H,R′ is phenyl) and the formula —CR═NR′ including, for example,phenyl-N-methylimino, methyl-N-methylimino and phenyl-N-phenylimino

Unless otherwise specifically defined, “amide” refers to the generalformula —CONRR′ including, for example, N,N-dimethylaminocarbonyl,N-butylaminocarbonyl, N-phenylaminocarbonyl, N,N-diphenylaminocarbonyland N-phenyl-N-methylaminocarbonyl and to the general formula —NRCOR′including, for example, N-acetylamino, N-acetylmethylamino,N-benzoylamino and N-benzoylmethylamino.

Unless otherwise specifically defined, “ester” refers to the generalformula —CO₂R including, for example, methoxycarbonyl,benzoyloxycarbonyl, phenoxycarbonyl, naphthyloxycarbonyl andethylcarboxy and the formula—OCOR including, for example, phenylcarboxy,4-fluorophenylcarboxy and 2-ethylphenylcarboxy.

Unless otherwise specifically defined, “thioether” refers to the generalformula —SR including, for example, thiomethyl, thiobutyl andthiophenyl.

Unless otherwise specifically defined, “sulfonyl” refers to the generalformula —SO₂R including, for example, methylsulfonyl, ethylsulfonyl,phenylsulfonyl and tolylsulfonyl.

Unless otherwise specifically defined, “alkoxy” refers to the generalformula —O-alkyl including, for example, methoxy, ethoxy,2-methoxyethoxy, t-butoxy. Unless otherwise specifically defined,“aryloxy” refers to the general formula —O-aryl including, for example,phenoxy, naphthoxy, phenylphenoxy, 4-methylphenoxy.

Unless otherwise specifically defined, R and R′ are each independentlyselected from hydrogen, alkyl, substituted alkyl, heteroalkyl, aryl,substituted aryl, heteroaryl and substituted heteroaryl. Substituentgroups useful in the invention are those groups that do notdeleteriously affect the desired properties of the inventive compound.Substituent groups that do not deleteriously affect the desiredproperties of the inventive compound include, for example, alkoxy,alkyl, halogen, —CN, —NCS, azido, amide, amine, hydroxy, sulfonamide andlower alcohol.

The rigid backbone polymers described above could be used in various“forms” in the subject orthodontic invention. In one embodiment thepolymers might be used alone as neat resins. In this embodiment,variations of the rigid-rod, segmented rigid-rod or semi-rigid backboneand the solubilizing groups may be desirable to achieve preferredbalances of properties.

In another embodiment, rigid backbone polymers can be mixed with any orall of additives, filler materials, plasticizers and reinforcing agents.The resulting compounds have properties that can be tailored to thedesired end use. It should be noted that filler materials are added to apolymer matrix predominately to improve wear, alter color or reducefriction of the resulting material. Strength enhancement, whilepossible, is generally limited with filler material additions.Reinforcing agents such as glass fibers or carbon fibers are addedprimarily to improve strength properties of the resulting material,sometimes by two or three times the unreinforced strength. Eitherchopped or continuous reinforcing fibers can be used. The improvement inproperties generally increases with the aspect ratio of the fibers.However, reinforcing fibers have several disadvantages, particularly forthe inventive orthodontic application. Desirable isotropic propertiesare lost when using continuous reinforcing fibers. If manipulation oforthodontic components is necessary, such as arch wire adjustments orforming of springs, loops or other desirable shapes, fibers may shiftfrom a uniform, homogeneous distribution, deteriorating mechanicalproperties. In some inventive variations an orthodontic componentconsists essentially of a rigid backbone polymer and no more than 5% byweight of a reinforcing agent. As used herein, “an orthodontic componentconsisting essentially of a rigid backbone polymer and no more than 5%by weight of a reinforcing agent” means that the orthodontic componentcontains no more than 5% by weight of materials intended primarily toincrease the mechanical properties of the polymer.

In a further embodiment, at least one rigid backbone polymer can be usedas an effective, molecular reinforcing component in other engineeringthermoplastics. For example, a polyphenylene polymer could be blendedwith other engineering thermoplastics, such as polycarbonate. Blendingresults in a physical mixing of two distinct polymer chains, for examplea rigid-rod polymer chain and a non-rigid-rod polymer chain such aspolycarbonate. Blending and polymer blends are intended to encompass allmethods of achieving such physical mixing including, for example,coreaction of different monomers to form blended homopolymers. Suchpolymer blends can yield desirable properties with even smallpercentages of the polyphenylene polymer. In blends, the combination ofthe rigid backbone polymer with one or more flexible non-rigid backbonethermoplastic produces what is sometimes referred to as a molecularcomposite, wherein the rigid backbone molecules are analogous to fibersin a conventional fiber-reinforced composite. However, since molecularcomposites contain no fibers, they can be fabricated much more easilythan fiber-reinforced composites and should be more amenable to formingin an orthodontic clinical setting.

Molecular composites present problems due to the limited solubility andfusibility of the rigid-rod structures and phase separation (in blends)from the more flexible non-rigid backbone polymer. However, theliterature teaches that use of the solubilizing groups and/ornon-parallel meta-phenylene backbone structures described abovealleviates the solubilizing and fusibility problems by somewhatdisrupting the regular paraphenylene structure. To address the problemof phase separation, U.S. Pat. No. 5,869,592, the contents of which areincorporated by reference herein, describes the addition of reactiveside groups to the phenylene macromonomers that chemically bind therigid-rod structure to the flexible polymer and help insure maintenanceof a uniform distribution of the rigid and flexible units, i.e. auniform blend is maintained and phase separation is avoided. Suchreactive side groups can be defined as compatibilizing side groups.

If many crosslinks are made between the rigid-rod polymer and theflexible polymer the resulting highly crosslinked structure will likelyresemble a thermoset and should be processed accordingly. At the otherextreme, if only a few reactive side groups per rigid-rod polymer chainare available to form crosslinks, a thermoplastic structure resembling agraft copolymer results. A non-limiting list of flexible polymers thatcan incorporate a rigid backbone polymer includes polyacetal, polyamide,polyimide, polyester and polycarbonate.

A molecular composite can also be formed by co-polymerization of arigid-rod and non-rigid-rod polymer units. In co-polymerization therigid-rod and non-rigid-rod polymer units are chemically bound. Therigid-rod molecules are analogous to fibers in fiber reinforcedcomposites. However, since molecular composites contain no fibers, theycan be fabricated much more easily than fiber-polymer composites andshould be more amenable to forming in an orthodontic clinical setting.The rigid-rod and non-rigid-rod monomer units can have various moleculararchitectures including, for example, a crosslinked polymer, a graftco-polymer or a semi-interpenetrating network.

In other embodiments, the rigid backbone polymer finds use as apost-polymerization additive. As a post-polymerization additive a rigidbackbone polymer may be used in compounding, blending, alloying, orotherwise mixing with preformed polymers, preformed blends, alloys ormixtures of polymers. In these cases the solubilizing side groups and/orreactive side groups help make the rigid-rod polymer compatible with thenon rigid-rod polymer to be reinforced. Such compounding, blending,alloying, etc. may be done by solution methods, melt processing,milling, calendering, grinding or other physical or mechanical methods,or by a combination of such methods.

Some properties of the above rigid backbone polymers are listed in Table2. It should be noted that the properties listed in Table 2 are for neatpolymers. As used herein, a neat polymer consists of a polymer resinwith essentially no other materials. A neat resin does not include, forexample an additive, a filler, another polymer resin, a plasticizer or areinforcing agent. Naturally, rigid backbone polymers when combined withfillers and/or reinforcing agents can provide even greater mechanicalproperties.

TABLE 2 rigid-rod semi-rigid-rod Property polymer polymer density(g/cm³) 1.21 1.23 refractive index 1.71 1.66-1.70 glass transition 160165 temperature (° C.) tensile strength (MPa) 207 207 tensile modulus(GPa) 10.3 8.3 flexural strength (MPa) 310 310 flexural modulus (GPa)9.7 8.3 elastic deformation 32 37 hardness, Rockwell B 89 80 hardness,pencil ≧9H 7h

As can be seen from Table 2, the rigid backbone polymer materialsunexpectedly have suitable properties in the unreinforced condition forclinical movement of teeth. In fact, according to calculations forstiffness, in orthodontic applications a 0.53 mm×0.69 mm (0.021inch×0.027 inch) unreinforced Parmax® 1200 wire would function like a0.41 mm (0.016 inch) diameter beta titanium wire; a 0.56 mm (0.022 inch)diameter unreinforced Parmax® 1200 wire would function like a 0.36 mm(0.014 inch) diameter beta titanium wire and a 0.48 mm (0.019 inch)diameter unreinforced Parmax® 1200 wire would function like a 0.41 mm(0.016 inch) diameter nickel-titanium wire. In some inventive variationsan orthodontic component can be prepared consisting essentially of arigid backbone polymer. As used herein, “an orthodontic componentconsisting essentially of a rigid backbone polymer” means that theorthodontic component does not contain any material in the polymermatrix that would affect the desirable properties of the neat rigidbackbone polymer.

The advantageous combination of high strength, high modulus and highelastic deformation (flexural strength/flexural modulus) properties ofrigid backbone polymers make them desirable for use as inventiveorthodontic force delivery components such as the wires 12, 24 shown inFIGS. 1 and 3 respectively.

Some rigid backbone polymers have completely amorphous structures sothat their strength related properties are isotropic. No orientation ofthis type of polymer is necessary to achieve desired strengthproperties. Rigid backbone polymer isotropy is desirable as it easesmanufacture of the inventive orthodontic components. Further, theinventive orthodontic components have relatively constant properties inall directions easing use of the inventive components. Naturally, otherinventive orthodontic components comprising rigid backbone polymersincorporating a reinforcing agent may exhibit anisotropic strengthproperties depending on the reinforcing agent if desired for aparticular application.

An important property of an orthodontic force delivery component isresistance to creep or minimal stress relaxation. Traditional polymerscan exhibit high elastic deformation, however, loads under the yieldstrength cause permanent deformation over time making them unsuitablefor both bracket and wire applications. A surprising property of rigidbackbone polymers is their creep resistance and their ability not todeform over time.

Another advantageous property of rigid backbone polymers is hardness. Ascan be seen from Table 2, rigid backbone polymers can have hardnesses ofup to about 80 to about 89 on the Rockwell B scale. These rigid backbonepolymer hardness values are among the highest of any thermoplasticpolymer material. These hardness properties make rigid backbone polymershighly scratch and abrasion resistant and provide exceptionally goodwear characteristics.

Rigid backbone polymers can range from almost transparent to atranslucent light yellow in color. As can be seen from Table 2, therefractive index of two exemplary rigid backbone polymers ranges from1.66 to 1.71, closely matching the 1.66 refractive index of toothenamel.

Inventive orthodontic components produced from a rigid backbone polymermaterial have an intrinsically pleasing aesthetic appearance. In someembodiments, a rigid backbone polymer can also be blended with dyes,filler materials or other additives to impart a desired color to theinventive orthodontic component produced therefrom allowing, forexample, a close approximation to tooth coloring and great aestheticacceptance. It should be understood that inventive orthodonticcomponents composed of a rigid backbone polymer can be evenly coloredthroughout their extent. Thus, the inventive orthodontic components arenot susceptible to peeling or wear through of surface coatings.

In another embodiment of the invention a rigid backbone polymer can bemolded over an insert to provide a composite orthodontic component.Alternatively, a rigid backbone polymer can be coated over anorthodontic component. The rigid backbone hardness properties make suchcomposite components and coatings more resistant to wear than knowncoatings.

Rigid backbone polymers are thermoplastic and can be thermally processedby, for example, injection molding, compression molding or extrusion.Typical compression molding conditions are about 300° C. to about 350°C., with pressures of about 0.689 MPa (100 psi) using either polymerpowder or pellets. Injection molding is also believed to be a viablethermal processing method for some rigid backbone polymers. Thus,another aspect of the invention is fabrication of these polymers into anovel orthodontic component or a novel orthodontic component precursorusing known thermoplastic polymer thermal processing techniques. As oneexample, inventive force delivery components 26, 28, 30, 32 havingdifferent cross sectional shapes such as shown in FIGS. 4 a-4 drespectively can be formed by extrusion. In another variation, thethermoplastic nature of rigid backbone polymers allows the creation ofvariations in cross sectional configuration, e.g., cross sectional sizeand shape. For example the wire 34 diameter can change along its lengthas shown in FIG. 5 a or the wire 36 can twist along its length as shownin FIG. 6. This feature is desirable since orthodontic biomechanics aremore dependent on appliance geometry than material mechanicalproperties, i.e., stiffness and maximum force vary with a power of thecomponent dimension, but only linearly with material mechanicalproperties. Thus, varying the cross-sectional configuration of aninventive wire along its length allows greater flexibility in design ofan orthodontic force system than is presently possible. The efficiencyof an orthodontic appliance depends on the magnitude of force producedand its constancy of action during tooth movement. This in turn isdependent in part on having a good fit between the orthodonticcomponents, for example between wire and bracket. Varying the crosssection along a wire allows for force control in three dimensions andoptimal fit or play between the wire and attachment depending on theindividual requirements of a patient.

The thermoplastic nature of rigid backbone polymers further allowssecondary thermal forming of orthodontic component precursors orprefabricated orthodontic components. For example, an orthodonticprecursor comprising a straight section of extruded rigid backbonepolymer can be thermal processed between rolls to provide a shapesimilar to the wire 26 in FIG. 4 a. As another example a novelprefabricated orthodontic component can be thermally formed to modifythe component shape and produce inventive orthodontic components withcomplex shapes such as the auxiliary 44 shown in FIG. 5 b and theligating spring 40 shown in FIG. 11. Such forming procedures can allowdental personnel to form or modify the inventive orthodontic componentsfor subsequent placement by an orthodontist.

Novel orthodontic components such as a bracket (38, 39 in FIGS. 7 and 8respectively) or tube (42 in FIG. 12 a) comprising a rigid backbonepolymer can be formed by, for example, compression molding or injectionmolding. The inventive brackets can include many novel slotconfigurations, for example the embodiments shown in FIGS. 7 and 8. Theslot 46 configuration in FIG. 7 allows interengagement with an inventivewire 48 having a keystone shape. Interengagement may be maintained withwires of different thickness, e.g. base to opposing arcuate crown. Theslot 50 configuration in FIG. 8 allows interengagement with inventivewires 52, 54 or 56 having different shapes. Multiple wires, for examplewire 54 and wire 56, can also be used together in slot 50. The inventionalso envisions interengagement of other orthodontic components, forexample, ligation caps or ligation mechanisms.

Interengagement of the slot, for example 46, and wire, for example 48,provides a good fit between the bracket slot and wire, therebydecreasing play between the bracket slot and wire. As used herein, agood fit between the wire and bracket means the wire, when inserted intothe bracket, is restricted to a rotational movement around the wirelongitudinal axis of no more than about plus or minus 5 degrees.Further, interengagement of the wire and bracket slot allows the samebracket to be a good fit with wires of different sizes andconfigurations, for example wire 56 or wire 54 in slot 50. In use, abracket is attached to a tooth and a first wire having a first crosssection is interengaged to provide a first desired orthodontic forcesystem. Subsequently, the first wire can be removed and a second wirehaving a cross section different from the first cross section isinterengaged in the same bracket to provide a different desiredorthodontic force system. Similarly, subsequent wires of diffent crosssections could be employed. Since each wire will interengage with thesame bracket slot to provide a good fit, control of the orthodonticforce system is not lost when the wire is changed. A conventionalbracket can, at best, provide a good fit with only a single conventionalwire size. Thus, this aspect of the invention functions to providegreater control of the orthodontic force system than is presentlypossible using conventional wires and brackets.

Orthodontic components such as restraining cap 60 shown in FIG. 9comprising a rigid backbone polymer can be formed by, for example,extrusion, compression molding or injection molding. The novelrestraining cap 60 is configured to clamp around the tie wings 62 of abracket and secure a force delivery component 12 within the bracketslot. The configuration of the restraining cap 60 allows the cap toslide over the tie wings 62. Alternatively, the restraining cap 60 issufficiently resilient to elastically expand as it is pushed over thebracket, and contract when the locking arm 64 moves under the tie wing62, securing the restraining cap 60 to the bracket and maintaining theforce delivery component within the bracket slot.

The rigid backbone polymer materials can be machined and finished onstandard equipment to form inventive orthodontic components. Typically,rigid backbone polymer materials can be machined in a manner similar toaluminum with a resulting surface finish also similar to aluminum. Toolsand techniques designed for plastics or laminates can also successfullybe used with rigid backbone polymer materials. It should be noted thatmost metalworking fluids can be used with rigid backbone polymersincluding mineral oils that would dissolve or attack other polymers.

Advantageously, inventive orthodontic components can be bonded to eachother using heat or adhesives, for example a dimethacrylate basedadhesive. Orthodontic components comprised of rigid backbone polymersare believed to be bondable to a tooth enamel surface using commerciallyavailable orthodontic adhesives such as TRANSBOND available from3M-Unitek. Some form of mechanical retention, i.e. undercuts orroughening, designed into the orthodontic components would beadvantageous to achieve bonding between the components and tooth enamel.Bondability of the inventive components is desirable to allowflexibility in design of the orthodontic force system. A restraining cap60 can be bonded at selected locations along the length of a wire 12 toform an integral restraining cap and wire 66 as shown in FIG. 10.

It should be understood that the following examples are included forpurposes of illustration so that the invention may be more readilyunderstood and are in no way intended to limit the scope of theinvention unless otherwise specifically indicated.

Example 1 Properties of Rigid Backbone Brackets

Orthodontic brackets 68 as shown in FIG. 14 were machined from acompression molded plaque of random copolymer of benzoyl appended1,4-phenylene (15 mol % of the repeat units) and 1,3-phenylene (85 mol %of the repeat units) (available as Parmax® 1200 from Mississippi PolymerTechnologies, Inc.). The orthodontic brackets 68 had four differentbracket wall thicknesses; 0.51 mm, 0.99 mm, 1.5 mm and 2.0 mm (0.020,0.039, 0.059 and 0.079 inch). Polycarbonate brackets with identicaldesign were used as a control. A 0.53 mm×0.64 mm (0.021×0.025 inch)stainless orthodontic wire was twisted in the bracket slot until failureof the bracket occurred. Moments were continuously monitored with atorque gauge. As shown in FIGS. 15 and 16, the rigid backbone (Parmax®1200) brackets 68 showed a significant improvement in both stiffness andthe maximum moment at failure as compared to the polycarbonate bracket.

Example 2 Properties of Rigid Backbone Force Delivery Components

Orthodontic wires were fabricated from a compression molded plaque ofpoly-1,4-(benzoylphenylene) (available as Parmax® 1000 from MississippiPolymer Technologies, Inc.) and a random copolymer of benzoyl appended1,4-phenylene (15 mol % of the repeat units) and 1,3-phenylene (85 mol %of the repeat units) (available as Parmax® 1200 from Mississippi PolymerTechnologies, Inc.) by machining to a dimension of 0.53 mm×0.64 mm(0.021 inch×0.025 inch). A 5 millimeter wire span length simulating anintra-oral inter-bracket distance was loaded using a cantilever test. Atorque gauge recorded the moment at the attached end of the wire.Polycarbonate wires were used as a control. The test data clearlydemonstrates the ability of the rigid backbone (Parmax® 1000 andParmax®1200) wires to deliver sufficient force, low force-deflectionrates, and a large elastic deflection needed for orthodontic toothmovement (FIGS. 17 and 18). The polycarbonate wires by comparisondelivered forces that were too low to produce desired tooth movement.

Example 3 Permanent Deformation of Rigid Backbone Orthodontic Wires

A straight section of orthodontic wire with dimensions of 0.021inches×0.025 inches was cut from a compression molded plaque ofpoly-1,4-(benzoylphenylene), (available as Parmax® 1000 from MississippiPolymer Technologies, Inc.) using a slow speed diamond saw. The wire waspositioned into two misaligned orthodontic brackets. The edge-to-edgeand center-to-center interbracket distances were 7 mm and 11 mm,respectively. The brackets were misaligned 3 mm in the apical-occlusaldirection. There was no rotation in the brackets. The wire was removedafter 1, 2 and 3 hour intervals. The apical-occlusal permanentdeformations within the 7 mm interbracket region at the three timeperiods were 0.0 mm, 0.24 mm and 0.14 mm, respectively. There was noindentation of the rigid backbone (Parmax® 1000) wire, indicating thatthe wire had sufficient hardness. There was no discoloration or whiteregions at critical sections of the rigid backbone wire indicating nofailure of the wire had occurred.

Example 4 Water Immersion

A free-end cantilever test was used to evaluate flexural propertiesbefore and after water immersion. Materials tested werepoly-1,4-(benzoylphenylene) (available as Parmax® 1000 from MississippiPolymer Technologies, Inc.) and a random copolymer of benzoyl appended1,4-phenylene (15 mol % of the repeat units) and 1,3-phenylene (85 mol %of the repeat units) (available as Parmax® 1200 from Mississippi PolymerTechnologies, Inc.). Polycarbonate (Tuffak™ available from Atohaas) wasused as a control.

Two samples of each material were prepared with dimensions of 0.53mm×0.64 mm×50.0 mm (width×thickness×length) to simulate an orthodonticwire. Samples were conditioned in an oven for 24 hours at 50° C. andcooled in a desiccator. Following conditioning, one sample of eachmaterial was placed in a capped vial filled with deionized water. Thevials were placed in a water bath maintained at 37° C. The second 50 mmlong sample of each material was maintained in a desiccator. Sampleswere removed from the desiccator at 5 days and from the water bath (andtowel dried) at 5 days, 30 days and 365 days and cut to lengths of 15 mmto accommodate a test span length of 5 mm. A free-end cantilever testwas used to measure flexural rigidity, moment at yield and displacementat yield. These properties are listed in Table 3.

TABLE 3 Parmax ® 1000 Parmax ® 1200 Polycarbonate Flexural Rigidity(g-mm/degree) Before Immersion 41 36 13  5 days 42 38 16  30 days 51 5322 365 days 62 43 18 Moment at Yield (g-mm) Before Immersion 950 933 300 5 days 883 858 325  30 days 708 650 279 365 days 942 875 325Displacement at Yield (degrees) Before Immersion 28 32 33  5 days 28 2828  30 days 14 14 13 365 days 17 23 28After 365 days of water immersion the Parmax® 1200 sample showed nochange in flexural rigidity or moment at yield but did exhibit apossible decrease in displacement at yield. After 365 days of waterimmersion the Parmax® 1000 sample showed no change in moment at yieldbut did exhibit a possible increase in flexural rigidity and decrease indisplacement at yield. The inventors believe that the changes could bedue to experimental error and even if real that the changes areclinically insignificant. As can be seen from the results of Table 3,the rigid backbone wires have surprisingly improved mechanicalproperties, both initially and after extended water immersion, whencompared to wires made of known polymer materials.

Example 5 Color Stability

A modified version of ANSI/ADA Specification No. 12 was used to comparethe color stability of polyphenylene polymers to standard polymers usedin orthodontics. Samples tested were poly-1,4-(benzoylphenylene)(available as Parmax® 1000 from Mississippi Polymer Technologies, Inc.);a random copolymer of benzoyl appended 1,4-phenylene (15 mol % of therepeat units) and 1,3-phenylene (85 mol % of the repeat units)(available as Parmax® 1200 from Mississippi Polymer Technologies, Inc.);polycarbonate (Tuffak™, available from Atohaas); and commercialorthodontic polyurethane “O-rings” (SoloTie-Clear™, available from ClassOne Orthodontics). Two samples of each material were made withdimensions of 0.53 mm×2.28 mm×15 mm to simulate the thickness of anorthodontic wire, except for the “O-rings” which were usedas-manufactured. One control sample of each polymer material was wrappedin aluminum foil and placed in a box to prevent exposure to light. Asecond sample for each polymer material was exposed to a combination ofwhite light from a standard 60-watt, 120-volt incandescent bulb and ablack light (Black-Ray Lamp model UVL-56, long wave UV-366 nm, 115volts, 60 Hz, 0.16 amps, UVP, Inc., San Gabriel, Calif.). Samples wereplaced on an aluminum plate, positioned 17.8 cm away from the lightsource, and exposed for 24 hours. Following exposure all samples werevisually compared to control samples. There were no visually detectabledifferences between the exposed rigid backbone polymers (Parmax® 1000and Parmax® 1200) and their controls; or the polycarbonate sample andits control. The exposed polyurethane sample (about 10 O-rings evaluatedas a unit) had a slight brown/yellow tint relative to their unexposedcontrols. As can be seen from the results, the rigid backbone sampleshave improved color stability when compared to some known orthodonticpolymer materials.

Example 6 Staining Resistance

Resistance to common staining agents was evaluated. Samples tested werepoly-1,4-(benzoylphenylene) (available as Parmax® 1000 from MississippiPolymer Technologies, Inc.); a random copolymer of benzoyl appended1,4-phenylene (15 mol % of the repeat units) and 1,3-phenylene (85 mol %of the repeat units) (available as Parmax® 1200 from Mississippi PolymerTechnologies, Inc.); polycarbonate (Tuffak™, available from Atohaas);and commercial orthodontic polyurethane “O-rings” (SoloTie-Clear™,available from Class One Orthodontics). Four samples of each materialwere made with dimensions of 0.53 mm×2.28 mm×15 mm to simulate thethickness of an orthodontic wire except for the “O-rings” which wereused as manufactured.

One sample for each polymer material was exposed to each of thefollowing three coloring agents: mustard, tea and red wine. To preparethe coloring agents, the mustard was mixed with deionized water at aratio of 1:5, one black tea bag was added to 250 mL of hot water, andthe red wine was used at full strength. One sample for each polymermaterial was exposed to deionized water and used as a control. Sampleswere immersed in the coloring agents for 24 hours and maintained at 37°C. Following exposure samples were blotted dry and visually compared tothe deionized water controls by three examiners. Relative to thecontrols the samples were scored as no different (−−), slightlydifferent (+), clearly stained (++), or dark staining (+++). Results ofthe staining comparison are shown in Table 3.

TABLE 4 Mustard Tea Red Wine Parmax ® 1000 −− −− −− Parmax ® 1200 + −−−− Polycarbonate + ++ +++ Polyurethane +++ +++ +++As can be seen from the results of Table 4, the rigid backbone sampleshave improved resistance to staining from contact with common food itemswhen compared to known orthodontic polymer materials.

Example 7 Creep or Stress Relaxation of Rigid Backbone Orthodontic Wires

Parmax® 1200 and polycarbonate wires were placed in two brackets withnon-aligned slots of 3 mm and an interbracket distance of 7 mm.Instantaneous measurement showed negligible permanent deformation ofboth wires. The load was maintained for 24 hours and permanentdeformation measured. The Parmax® wire had negligible deformation (0.3mm) and the polycarbonate wire showed 1.2 mm deformation, which was 40%of the total deflection.

Example 8 Extruded Rigid Backbone Orthodontic Wires

Five sets of 1.0 mm (0.040 inch) diameter round orthodontic wires wereextruded. Uniform round cross sections were maintained to a toleranceunder 10%. The extruded wires were neat Parmax® 1200, neat Parmax® 1000and one set of wires comprising Parmax® with a plasticizer. The wiresexhibited good aesthetics possessing translucency with a slight yellowtint.

A cantilever test was performed on 5 mm long specimens applying 750 g-mmload increments with a torque gauge until failure. The graph in FIG. 19shows adequate stiffness, approximately 200 g-mm/degree, for demandingorthodontic tooth movement. The maximum moment (moment at yield) waswithin a range of 3000-4500 g-mm allowing for the application of heavierorthodontic forces if required. This data illustrates that a Parmax®wire can be scaled down in size and still be capable of deliveringsufficiently high forces for efficient tooth movement if smallerattachments are used.

FIG. 19 also shows the remarkable high elastic deformation of theParmax® wires, which was between 10° and 15°. The extruded wiresdemonstrated good ductility with deflection in the plastic range aslarge as 50°. Ductility is important to prevent wire breakage underclinical conditions.

Example 9 Forming of Rigid Backbone Orthodontic Wires

Orthodontic wires were manipulated by hand to form selective curves andbends that would be necessary to form various orthodontic appliancedesigns. The wires were a 1.07 mm diameter extrusion of a randomcopolymer of benzoyl appended 1,4-phenylene (15 mol % of the repeatunits) and 1,3-phenylene (85 mol % of the repeat units) (available asParmax® 1200 from Mississippi Polymer Technologies, Inc.). The necessaryconditions for forming the wires were determined by heating the samplesto various combinations of temperatures and times in a laboratory oven.Samples 70 mm in length were heated at temperatures between 180° C. and200° C. for 5 to 20 minutes. Samples heated to 195° C. for at least 15minutes, or advantageously at 200° C. for 10 minutes or more, weresufficiently soft to be readily formed into desired orthodonticconfigurations. The forming had to be done quickly before the samplescooled to their unheated state.

Example 10 Forming of Rigid Backbone Orthodontic Archwires

Using a custom-made two-part aluminum mold an orthodontic archwire 72,as shown schematically in FIG. 20, was formed from a random copolymer ofbenzoyl appended 1,4-phenylene (15 mol % of the repeat units) and1,3-phenylene (85 mol % of the repeat units) (available as Parmax® 1200from Mississippi Polymer Technologies, Inc.). The shape was similar tothe upper medium Tru Arch™ (A Company) arch form. To prepare archwire 72generally straight lengths of the rigid backbone polymer were extrudedwith a diameter of approximately 1.0 mm. The arch shape was achieved inthree stages. First, a straight length of the rigid backbone polymer washeated to 200° C. for 15 minutes, removed from the oven and formed byhand to the approximate shape of the aluminum mold. Next, the precursorwire and mold were heated together at 200° C. for an additional 15minutes, removed from the oven and the sections of the mold were slidtogether to form the precursor wire closer to the desired shape. Themold and precursor wire were placed in the 200° C. oven for a final 15minutes, then allowed to bench cool for one hour before the wire wasremoved from the mold. Thereafter the wire 72 maintained the desiredarch shape.

Example 11 Reducing Rigid Backbone Wire Dimension to Fit OrthodonticBrackets

The cross-sectional dimension of straight lengths of a random copolymerof benzoyl appended 1,4-phenylene (15 mol % of the repeat units) and1,3-phenylene (85 mol % of the repeat units) (available as Parmax® 1200from Mississippi Polymer Technologies, Inc.) was reduced fromapproximately 1 mm (0.040 inch) to 0.53 mm (0.021 inch) to fit intostandard orthodontic brackets. This was achieved by clamping the rigidbackbone wire and 0.53 mm (0.021 inch) stainless steel spacers betweenaluminum platens heated to 200° C. The clamps were tightened after eachof four successive 15-minute heating periods. The assembly was allowedto bench cool for 20 minutes before the clamps and wire were removed.The inventive wire had two opposing flat faces connected by arcuatesides. This procedure was also applied to the archwire formed in Example10.

Example 12 Clinical Applications of Rigid Backbone Orthodontic Wire

A rigid backbone archwire 74 was inserted into two posterior buccaltubes 76, 78 as anchor units as shown in FIGS. 21 a, 21 b and 21 c.Ligature wires, elastomeric rings or elastic thread could be placed tomove anterior teeth in the desired direction. This includes overbitereduction, closing of open bites, tooth alignment or rotation and crossbite correction. Attachments could be placed as needed on the anteriorteeth.

FIG. 22 schematically illustrates upper and lower archwires, 80, 82respectively, inserted into upper and lower buccal tubes, 84, 86respectively. Ligature ties can be placed to move any of the teethanterior to the second molars that have attached tubes.

FIGS. 23 (before) and 24 (after) schematically illustrate an elasticattached to a rigid backbone polymer archwire to extrude a canine tooth.

FIGS. 25 (before) and 26 (after) schematically illustrate a segmental 1mm (0.040 inch) diameter rigid backbone polymer wire 100 used to uprighta tipped posterior segment. The inventive segmental wire 100 is attachedto a rigid esthetic anterior segment made of a fiber-reinforcedcomposite or suitable polymer.

Example 13 Clinical Applications of Rigid Backbone Aligners

The efficiency of an orthodontic tooth aligner can be enhanced with theuse of a rigid backbone polymer component. Current esthetic polymerswith lower modulus, yield strength and hardness than a rigid backbonepolymer lack the rigidity and shape stability to produce exacting detailin tooth alignment, particularly in the finishing stages of alignertreatment. Rigid backbone polymers with higher mechanical propertieswould be able to produce more exacting detailed alignment. For example,as shown in FIG. 27 most tooth movement requires varying deflection ofpoints on a tooth. Thus, variation in stiffness by using differentmaterials in a single aligner is desirable. The high stiffness of rigidbackbone polymers can be part of such a system. For example, if theinclination of a tooth requires correction wherein the root is movedlingually and the crown is maintained in its approximate initialposition, the high stiffness rigid backbone polymer is placed around theincisal-crown portion of the aligner and a low stiffness polymer isplaced apically in the gingival-crown region.

As a further example a rigid backbone polymer wire 108 can beincorporated into an aligner 110 as shown in FIG. 28 to improve toothmovement and anchorage control. In this application a rigid backbonewire is applied to the crowns of the teeth to produce detailed toothmovement. This wire is embedded in a lower stiffness aligner that servestwo purposes, to position the rigid backbone wire and to offer theremainder of the arch for anchorage.

Example 14 Evaluating the Effect of Time and Temperature on RigidBackbone Polymer Flexure Properties

Flexure tests were conducted on 1.17 mm diameter rigid backbone polymerwires to determine if the various time and temperature combinations usedin clinical forming affected mechanical properties of the formedcomponent. 50 mm long by 1.17 mm diameter wires of a random copolymer ofbenzoyl appended 1,4-phenylene (15 mol % of the repeat units) and1,3-phenylene (85 mol % of the repeat units) (available as Parmax® 1200from Mississippi Polymer Technologies, Inc.) were heated to 200° C. forperiods of 10 to 80 minutes and between 185° C. and 210° C. for 15minute periods. Each sample was allowed to bench cool and was cut intothree 15 mm long samples. The samples were tested as 5 mm cantileversrecording angular deflection and torque. As shown in the tables belowthere were no significant changes in flexure properties.

TABLE 5 constant temperature (200° C.) for various times FlexureDisplacement Moment Time rigidity at Yield at Yield (minutes)(g*mm/degrees) (degrees) (g*mm) control 383 8.2 3000 10 363 8.5 3000 20351 8.7 3000 30 343 8.8 3000 40 356 8.5 3000 50 357 11.3 3750 60 374 8.33000 70 368 8.3 3000 80 348 8.8 3000

TABLE 6 constant time (15 minutes) for various temperatures FlexureDisplacement Moment Temperature rigidity at Yield at Yield (° C.)(g*mm/degrees) (degrees) (g*mm) control 396 8.2 3000 185 352 8.2 3000190 383 8.2 3000 195 365 8.5 3000 200 351 8.7 3000 205 390 8.0 3000 210396 8.0 3000

While preferred embodiments of the foregoing invention have been setforth for purposes of illustration, the foregoing description should notbe deemed a limitation of the invention herein. Accordingly, variousmodifications, adaptations and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the presentinvention.

1. A method of forming an orthodontic archwire, comprising: providing athermoplastic material at least partially comprising a first arylene orheteroarylene moiety joined to a second arylene or heteroarylene moietyby a covalent bond between adjoining ring carbon atoms of the arylene orheteroarylene moieties; heating the thermoplastic material; andprocessing the heated thermoplastic material to form the orthodonticarchwire.
 2. The method of claim 1 wherein the covalent bond is a 1,4covalent bond.
 3. The method of claim 1 wherein the thermoplasticmaterial comprises a plurality of covalent bonds and wherein at leastabout 95% of the covalent bonds are substantially parallel to eachother.
 4. The method of claim 1 wherein the thermoplastic materialcomprises at least one of a compatibilizing side group or a solubilizingside group.
 5. The method of claim 1 wherein the thermoplastic materialcomprises the following structure:

wherein each of R1, R2, R3 and R4 is independently chosen from H or anyorganic solubilizing group.
 6. The method of claim 1 wherein thethermoplastic material comprises the following structure:

wherein each of R1, R2, R3 and R4 is independently chosen from H or anyorganic solubilizing group, and n is an integer from 2 to about
 8. 7.The method of claim 1, wherein the orthodontic archwire is formed todeliver an orthodontic force to the teeth of an individual when saidarchwire is engaged with said teeth.
 8. The method of claim 1, whereinthe processing step comprises thermal processing the heated material toprovide the orthodontic archwire having a different cross section atdifferent points along its length.
 9. The method of claim 1, wherein thethermoplastic material comprises a reinforcing agent.
 10. The method ofclaim 1, wherein the material consists essentially of a mixture ofthermoplastic rigid backbone polymers.
 11. The method of claim 1,wherein the material consists essentially of a mixture of thermoplasticrigid and non-rigid backbone polymers.
 12. The method of claim 1,comprising the steps of heating and processing the thermoplasticmaterial a second time to form the orthodontic archwire.
 13. The methodof claim 1, comprising the steps of heating and processing thethermoplastic material a second time to modify the orthodontic archwireshape.
 14. The method of claim 1, wherein the step of processingincludes one of the group consisting of extrusion, compression moldingand injection molding.
 15. The method of claim 1, wherein the step ofprocessing includes forming the archwire into a helical springconfiguration.
 16. The method of claim 1, wherein the step of processingincludes forming the archwire into a cantilever.
 17. The method of claim1, wherein the step of processing includes forming the archwire into acoiled spring configuration.
 18. The method of claim 1, wherein the stepof processing includes forming the archwire into a loop.
 19. The methodof claim 1, wherein the step of processing includes forming an archwirehaving a cross section that is not circular and not quadrilateral.
 20. Amethod of providing an aesthetically desirable archwire for use inorthodontic treatment of the teeth of an individual, comprising:providing a thermoplastic material at least partially comprising a firstarylene or heteroarylene moiety joined to a second arylene orheteroarylene moiety by a covalent bond between adjoining ring carbonatoms of the arylene or heteroarylene moieties; heating thethermoplastic material; and processing the heated thermoplastic materialto form the aesthetically desirable orthodontic archwire, wherein saidarchwire has a color that is similar to the color of said teeth of saidindividual.
 21. A method of providing an aesthetically desirablearchwire for use in orthodontic treatment of the teeth of an individual,comprising: providing a thermoplastic material at least partiallycomprising a first arylene or heteroarylene moiety joined to a secondarylene or heteroarylene moiety by a covalent bond between adjoiningring carbon atoms of the arylene or heteroarylene moieties; heating thethermoplastic material; and processing the heated thermoplastic materialto form the aesthetically desirable orthodontic archwire, wherein saidarchwire is generally colorless in appearance.